Particle therapy systems use an accelerator to generate a particle beam for treating afflictions, such as tumors. In operation, particles are accelerated in orbits inside a cavity in the presence of a magnetic field, and removed from the cavity through an extraction channel. A magnetic field regenerator generates a magnetic field bump near the outside of the cavity to distort the pitch and angle of some orbits so that they precess towards, and eventually into, the extraction channel. A magnetic field regenerator is typically a ferromagnetic arrangement that provides an enhancement to an existing magnetic field.
Heretofore, particle accelerators operated using a relatively low magnetic field, e.g., on the order of 2 Tesla. In such cases, the magnetic field bump produced by the magnetic field regenerator could “suck” a significant amount of the magnetic flux from the interior magnetic fields. This creates a magnetic field hole in the cavity relative to the background 2 Tesla magnetic field. This hole was typically filled by incorporating progressively smaller radially-adjacent magnetic field regenerators into the cavity to add progressively smaller magnetic field bumps in place of corresponding holes generated each by an immediately preceding magnetic field regenerator. Implementing the foregoing magnetic field correction using progressively smaller magnetic field regenerators can be difficult in systems that operate at relatively low magnetic fields.